Research Projects

Approved Research Projects for SKA SA Masters and Doctoral Bursary Students for 2018

When reviewing the approved projects for 2018, please ensure that you click on “View Project Proposal” just below the Project overview in order for you to see who the prospective Supervisor of the selected project is.

Masters Research Projects: Astronomy

Constraining the epoch of reionization with PAPER observations

Overview

The Precision Array to Probe the Epoch of Reionization (PAPER) has been a low frequency radio interferometer deployed at the Karoo site in order to observe the 21-cm emission from the epoch of reionization. Its final, 128-element (PAPER128) observing season was completed at the end of 2014 and its results will start to be published in 2018. Our group has been heavily involved in the analysis (PhD project of C.D. Nunhokee, to be completed at the end of 2017, Msc project of J. Chege, started in 2017).

With the analysis of the PAPER128 data well under way, we are seeking for an ambitious Msc candidate who is willing to become an observational 21-cm cosmologist. The candidate is expected to carry out simulations to investigate the impact of foreground and instrumental systematics on the PAPER128 power spectrum and to use state of the art theoretical codes to constrain the physics of reionization with PAPER128 power spectrum.

An ideal candidate will have a good background in physics and mathematics, the willingness to learn about advanced radio interferometry, statistics, signal processing techniques and cosmology, but, mostly, the desire to contribute to the 21-cm cosmology revolution.

The Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey is one of the approved MeerKAT Large Survey Projects with a goal to study the evolution in the neutral hydrogen gas, HI, content of galaxies over two-thirds the age of the universe. Given the low frequency and high sensitivity capabilities of MeerKAT, this survey will likely provide the most distant sample of HI detections in galaxies prior to the SKA becoming operational.

In order to extract information from the radio data beyond the directly detected galaxies, we plan to stack the HI spectra of galaxies identified from optical spectroscopy datasets in our field. Knowing the redshifts and expected positions of galaxies, we can identify where in the HI data cube their HI line emission, if it exists, should be located, even for signals below the noise level. We can then extract the spectra and co-add them with other HI spectra to obtain average properties of different sub-samples of galaxies. LADUMA team members have recently developed an HI stacking package for use by the astronomical community (Healy et al. 2017, in prep.) but we have further outstanding requirements for this software to enable the fast and efficient analysis of our data.

These requirements include: the development of fast and parallelized methods to extract thousands of spectra at varying resolutions from the large LADUMA data cube; the capability to run stacking analyses at different resolutions in parallel; parallelizing the uncertainty estimation method; and the development of a database to store stacking run input catalogues and parameters. The software development will also involve integration with the IDIA (Inter-university Institute for Data-Intensive Astronomy) cloud environment since the data will be located in the IDIA cloud. The software developed in this project will be integral to the HI stacking analyses of the LADUMA project.

The South African MeerKAT array is leading a new generation of telescopes that will observe the radio emission from distant galaxies to unprecedented depths. By combining many observations and using statistical techniques, information can be obtained that is beyond the detection limit of the individual observations themselves. This allows us to probe the properties of the very faintest galaxies.

One such technique is known as P(D), or probability of deflection. The name comes the time when radio astronomy relied on chart recorders, and the probability that the pen would deflect by a certain amount due to noise fluctuations was a useful indication as to whether a signal was real or not. The modern use of this technique still relies on measuring fluctuations, however the fluctuations are pixel values in an image. We also make use of a phenomenon called ‘classical confusion’ where the angular resolution of the instrument is no longer high enough to separate individual sources from one another. This occurs for MeerKAT at a depth of about 2 microJy/beam. We turn this limitation to our advantage. By driving the noise down to the level of the confusion limit, and studying the distribution of the pixel brightnesses in the image (the ‘deflections’) we can use a model of both the instrumental noise and the radio source population and constrain the properties of the latter.

This technique has been used in the past to constrain the properties of the faint radio source population, however the novel aspect of this project is that we stack up multiple observations over different regions of the sky. Using our knowledge of the instrumental response allows us to apply the P(D) test at very faint levels, circumventing the need to spend many hours of telescope observing time on a single deep observation.

Radio jets and bubbles from a rare Type 2 quasar in a brightest cluster galaxy

Overview

We have been awarded JVLA time to search for radio emission associated with a Type 2 quasar hosted by the brightest cluster galaxy (BCG) of the cluster ACT-CL J0320.4+0032 (J0320) at z = 0.384. J0320 is one of only a handful of BCGs known to host a Type 2 quasar, and presents a rare opportunity to understand the role played by quasar-mode feedback on the intracluster medium (ICM). Our Chandra and XMM-Newton observations reveal the presence of a shock or cold front feature within 35 kpc of the BCG, which Hubble Space Telescope observations have shown has a double nucleus. We also see hints of cavities in the X-ray emission, which could be associated with past or present AGN activity. We will use JVLA to map the cluster in the L and C bands, in order to search for evidence of jets or bubbles associated with the quasar, and determine the effect of any outflows on the ICM.

A central goal of current and future cosmological surveys is to uncover the nature of dark energy. The University of KwaZulu-Natal is leading the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) project, which will comprise a compact array of around 1,000 small (~6m) dishes operating between 400 and 800 MHz. The primary aim of HIRAX is to map baryon acoustic oscillations (BAOs) in the cosmological 21cm intensity distribution over a significant fraction of the sky between redshifts 0.8 and 2.5, and thereby place strong constraints on the dark energy equation of state. The HIRAX project offers students the opportunity to train on cutting edge science, engineering, analysis and big data techniques in a South African-led project. The relatively short time-scale for the full HIRAX survey makes it ideal for MSc and PhD projects. The project will also include student involvement in the analysis of data from the HIRAX 8-element and 128-element prototypes that will operate on the 1-2 year timescale.

A major challenge in uncovering the cosmological 21cm signal is the presence of galactic foregrounds that are several orders of magnitude above the signal but fortunately smooth in frequency in contrast to the 21cm signal. This project will focus on foreground subtraction techniques and the design of optimal estimators to extract the various 21cm cosmological signals, such as BAOs and lensing, in the presence of foregrounds and noise. The foreground challenge can be mitigated through cross-correlations with other large-scale structure tracers that will be available from other cosmological surveys e.g. LSST, that have independent noise and systematics. The key part of the project will involve applying these techniques to the HIRAX data to test their suitability and allow the student to build more robust and effective techniques, taking into account real effects that are seen in the data.

Several current or upcoming radio arrays are laid out on regular grids, such as PAPER, HERA, CHIME, HIRAX, and Tianlai. These arrays are searching for neutral hydrogen signals at high redshift such as those from the Epoch of Reionization (EoR), or intensity mapping at intermediate redshifts (z ~ 1 – 2) searching for the evolution of dark energy. These signals are faint, especially in comparison to the bright foreground emission of the Milky Way. The calibration requirements for these arrays are incredibly strict, since errors of 0.1% can lead to foreground emission leaking into the desired HI signal. Calibration techniques relying on the regular spacing of the array have been very successful, allowing PAPER to place stringent limits on the EoR signal. However, no physical array will ever be perfectly redundant, and so going forward we will need to account for array non-idealities in order for these projects to realize their full potential.

One new technique to calibrate more realistic arrays is calibration via the correlation function (Sievers 2017), which provides a natural framework for incorporating more realistic array properties into the calibration. In simulations, corrcal makes significant improvements on the calibration of arrays with realistic non-idealities, but several natural extensions have yet to be tested. This project will apply corrcal to existing datasets, possibly including PAPER, HERA, or the currently-operating HIRAX prototype, and extend it so that it can be used to characterize important information about these arrays.

The MeerKAT array will probe the radio universe at an unprecedented sensitivity and with very wide frequency coverage. Its increased sensitivity has to potential to refine our understanding of the Universe and the morphology of radio sources in particular. However, current CLEAN based imaging techniques are suboptimal in recovering the finer details of extended radio sources and may even introduce spurious features which, because of the lack of uncertainty information, can’t be distinguished from real ones. This project will leverage recent advances in Bayesian imaging and compressive sensing techniques to produce high quality continuum images along with uncertainty maps that can be used to gain a deeper understanding of what the Universe looks like in radio frequencies. The proposed formalism rephrases imaging in terms of a statistical inference problem and uses a mixture of variational inference and sampling techniques to extract statistically optimal information from the observed data. The robustness of the Bayesian approach has been illustrated with the Resolve package which has recently also been incorporated into the DDFacet imager.

The primary aim of this project would be to investigate the possibility of utilising the Bayesian evidence (for example by using the Polychord sampler) in conjunction with compressive sensing techniques to derive statistically optimal imaging algorithms. It will address questions such as: “What is the optimal dictionary to use for a specific image or class of images?”, “Can we let the data tell us what the value of the Lagrange multiplier should be?” and “How real is that feature in the image?”. The secondary aim of this project would be to investigate the numerous ways in which these computationally expensive algorithms can be used in conjunction with existing techniques to make them more practical (e.g. by formulating them purely in the image domain as minor cycle algorithms).

The study of the faint radio universe has recently become a very active field of research not only because of the promise of transformational capabilities of the SKA on this field, but also because of the major steps being taken and planned with SKA pathfinders and precursors. Upcoming radio surveys with the South African SKA precursor MeerKAT (2017-­) and with the SKA1 (2020-­) will routinely detect radio emission from Star Forming Galaxies (SFG) and Active Galactic Nuclei (AGN) up to high redshifts over large areas of the sky. Such data will dramatically improve sample sizes allowing us to trace the evolution of these radio source populations over cosmic time. In advance of completion of MeerKAT and the SKA1 one can make the first steps in this investigation using existing deep radio datasets both to do science along the way and to develop and test the algorithms required for their analysis.

To that end, the deepest existing data from GMRT 600 MHz wide-­area surveys led by Prof Taylor are in hand, covering well-­studied fields with deep and homogeneous ancillary data, spanning frequencies from 150 MHz right up to 10 GHz, in both polarization and total intensity. Ongoing and future LOFAR, GMRT, MeerKAT and JVLA survey programs including the MIGHTEE survey will soon expand upon current capabilities and pave the way for SKA1 science by producing deep surveys of the radio sky detecting millions of faint radio sources.

A key requirement to fully exploit upcoming radio continuum surveys is advanced algorithms for the automatic classification and characterization of very large numbers of radio sources using multi-­wavelength (ultraviolet, optical, near infrared, far-­infrared, sub-­millimeter) data. This is an area where machine learning techniques have recently led to rapid progress, thanks to large homogeneous multi-­wavelength datasets, faster computing facilities and improved algorithms.

Masters Research Projects: Engineering

Numerical electromagnetic analysis for radio astronomy antennas

Overview

Numerical electromagnetic analysis has become an indispensable tool in modern antenna design. The design of the mid-frequency aperture array and other radio astronomy antennas involves very large computational electromagnetics analyses. In such cases the computational cost can quickly become prohibitive and it becomes necessary to investigate more efficient numerical methods. For this project, the candidate must firstly study cutting-edge integral equation-based methods relevant to electrically large antennas. Secondly, the latest research work (at SU and at other international research institutions) on efficient analysis methods relevant to radio astronomy antennas must be implemented as a computer code, evaluated and further refined. Thirdly, the work must be applied to the analysis of SKA-relevant radio astronomy antennas. This challenging project has excellent scope for publication and can serve as a platform for further, advanced studies.

Probing Radio Intensity at high-Z from Marion (PRIZM) is an experiment that will study cosmic dawn in the universe using low frequency (< 150 MHz) observations of redshifted 21-cm emission from neutral hydrogen. The experiment, which is illustrated in Figure 1, is unique in that it comprises two small antennas that observe the 21-cm signal averaged over a large fraction of the visible sky. Measuring this global signal as a function of frequency/redshift opens a new window into a part of the universe’s history that is very poorly understood.
One of the greatest challenges in probing cosmic dawn at low frequencies is terrestrial radio frequency interference (RFI), which swamps the cosmological signal even when the nearest RFI sources are hundreds of kilometres away. PRIZM has been funded by the South African National Antarctic Programme (SANAP) for deployments to Marion Island, which lies 2000 km from the nearest continental land masses and offers an exceptionally clean RFI environment. PRIZM was successfully installed on Marion Island during the April 2017 takeover voyage, and the instrument is continuing to observe throughout the Austral winter.

Given the small scale of PRIZM, the student who takes on this project will be able to contribute to a wide range of work spanning both instrumentation and analysis. The student may have the opportunity to participate in the April 2018 voyage to Marion Island, where we will perform on-site instrument characterisation and possibly install new antenna hardware. The student will also have opportunities to analyse data from the 2017 winter observations and develop new low-frequency antenna hardware for future Marion deployments.

An exciting frontier of radio astronomy is using the redshifted 21-cm emission of neutral hydrogen to reconstruct a three-dimensional map of large-scale structure in the universe. These maps encode a faint imprint, known as baryon acoustic oscillations (BAOs), that correspond to remnant ripples left behind by sound waves echoing through the plasma of the early universe. Measurements from upcoming experiments will constrain BAOs with exquisite precision, opening new views into structure formation and the universe’s expansion history, and shedding light on the mystery of dark energy. We are in the initial stages of building a new radio telescope array called the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX)1. HIRAX will measure BAOs by mapping the entire southern sky over a frequency range of 400–800 MHz, and the experiment will be sited in South Africa. The project is complementary to the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which is about to begin surveying the northern sky. HIRAX has received seed funding, and an eight-element prototype array is currently under construction at HartRAO (Figure 1). The student who takes on this project will focus on the assembly and characterisation of this eight-element array. This prototype is a critical milestone along the path to constructing the full science array, consisting of 1024 elements. The student will characterise various receiver elements on the eight-element array, including active feeds, RF over optical fibre modules, and other subsystems that are currently under development. The work will include a combination of instrumentation assembly and testing, as well as data analysis. The results will be used to refine HIRAX subsystem design in preparation for the final science array.

Remote controls pose a threat of Radio Frequency Interference (RFI) to the SKA operation. This is because they are intentional transmitters that operate at a single frequency (typically in the 433MHz ISM band). Since they are used within range from the telescopes it is important to mitigate its potential radiation and influence on the scientific results.

It is proposed to review the technologies of low emission Internet of Things (IoT) nodes as these use spread spectrum and low data rates for signal transfer. This technology is also known as LPWAN (Low Power Wide Area Network). Typical examples are LoRa and SigFox. Measurements will be taken as case studies. Depending on the circuit topology and measurement results, possible solutions would be investigated. The purpose of this study is not to design and build a new type of remote control for production but rather use appropriate existing development kit units and use them in “quiet” modes for operation close to the SKA. Various LPWAN development kits are available and should be utilised for research before dedicated low cost remotes and receivers are developed. The outcome of this study would be a list of appropriate technologies (with pro’s and con’s) for use as low radiation signature remote / receiver combinations backed up by real life measurements.

Determination of the Influence of Commercial Lighting Emissions on the SKA

Overview

Energy saving lighting pose a threat (Radio Frequency Interference or RFI) to the SKA operation. Since lighting is installed in buildings within range from the telescopes it is important to determine its potential radiation signature and influence on the scientific results. These lighting RFI signatures will be paramount when using artificial intelligence (AI) to sift through observance data.

It is proposed to review light emitting diode (LED) and compact fluorescent lighting (CFL) technologies. Commonality between these configurations will give generic RFI signatures which are emitted from the power cables. It is proposed to measure conducted powerline emissions, model the power line as an antenna and calculate the emissions and signatures, while comparing to measured emissions. Once the RFI generation of the lamps has been determined, its influence on the SKA can be estimated. If possible, telescope time can be used for measuring lamps at distances for verification. Initial indications are that direct line of sight lamps in the 100km range will be visible to the SKA.

The specific aim of this study is twofold:

To determine an emission level / distance profile to know at what range LED and CFL lighting will interfere with the SKA science.

To determine and describe the typical RFI profile (signature spectrum) from a modern lamp so that the SKA AI filters can detect and remove it from the observations.

Solar plants pose the threat of Radio Frequency Interference (RFI) to the SKA operation. This is because they contain switching power electronics as well as digital control electronics. Since they will be installed within range from the telescopes it is important to mitigate its potential radiation and influence on the scientific results.

It is proposed to review the technology of solar plants, power electronic topologies and radiation mechanisms. Measurements will be taken as case studies and as “before” results. Depending on the circuit topology and measurement results, possible mitigation solutions would be investigated. This can include pulse shaping, filtering and screening. The purpose of this study is not to design and build a new type of solar inverter but rather use appropriate existing units and “quiet” them for operation close to the SKA. Of particular interest would be the DC filters from the solar panel supply as they are usually omitted in a normal industrial design but act as RFI antennae.

Mitigation solution/ solutions will be implemented and measured for “after” results.

Electric fences pose the threat of Radio Frequency Interference (RFI) to the SKA operation. This is especially true if the fence arcs. Since electric fences are installed within range from the telescopes it is important to mitigate its potential radiation and influence on the scientific results.

It is proposed to review the technology of electric fences, power electronic topologies and radiation mechanisms. Measurements will be taken as case studies and as “before” results. Depending on the circuit topology and measurement results, possible mitigation solutions would be investigated. This can include pulse shaping, filtering and arcing detection.

Mitigation solution/ solutions will be implemented and measured for “after” results.

The specific aim of this study is twofold:

To determine the mechanisms of radiated emissions of electric fences and its influence on the SKA.

To develop circuitry / sub-systems to mitigate RFI especially when a fence arcs.

Optical fibre technology forms the buried backbone of both MeerKAT and SKA. Both telescopes rely on highly stable clock tones to be distributed over optical fibre to each individual antenna. These clock signals are crucial for driving the digitizers, timestamping the data, and for monitoring and control functions. Complex interplay between a plethora of effects causes instability in the phase of a lightwave clock tone as it propagates within an optical fibre. These effects include temperature fluctuation, birefringence, polarization instability, component noise and others. The project aims to identify and quantify all such individual effects and investigate the complex interplay between them. A full suite of measurement and characterization techniques (including polarimetric, phase noise, time domain etc.) relevant to both the MeerKAT and SKA clock distribution systems will be used.

Recent advances in computational software packages enables the combined mechanicalelectromagnetic analysis of arbitrary structures. Previous studies have been focussed on the deformation of large dish reflector telescopes under the influence of gravitational loading using structural analysis techniques based on the finite element method (FEM). The purpose of this work is to build on that research, with particular focus on the effect of wind-loading on the antenna elements planned for the LFAA and MFAA when operating in an environment such as the Karoo in South Africa. In this case, a computational fluid dynamics (CFD) approach will be required. In both cases, the effect of the structural deformations on the electromagnetic performance of the structure will be analysed using computational electromagnetic (CEM) software offered by commercial solvers (such as FEKO).

Finite antenna array structures such as the Low-Frequency Aperture Array (LFAA) and Mid Frequency Aperture Array (MFAA) will consist of many array elements. The focus of this research is to use Machine Learning algorithms such as Support Vector Machines (SVM) to detect (and predict) array element failure. This includes locating the failed element, as well as categorizing the level of failure.

The SKA Mid-Frequency Aperture Array (SKA-MFAA) is part of Phase 2 of the SKA instrument, provisionally scheduled for deployment in the mid-2020s. The instrument will use aperture arrays, covering the frequency band from approximately 500-1500 MHz. It will be a very wide field of view instrument, characterized by electronically steerable beam(s). A presentation at the recent MFAA/MIDPREP meeting (Cape Town, April 2016) proposed that “tiles” be made available to South African educational institutions. These will probably be based on developments to the EMBRACE tile, which is the basic building block of the system, consisting of 72 Vivaldi antennas (6x6x2 polarisations) (Torchinsky et al, A&A, 2016). The system uses a hybrid beam-forming strategy, with the first stages done in RF using beam-former chips and subsequent stages done using digital beamforming. The system supports two independent RF channels, permitting two independently steerable beams on the sky.

The aim of this project is to commission such a system, after integrating it with a suitable Digital Back End (DBE) processor, such as a ROACH board. (EMBRACE uses custom-made DSP hardware based on LOFAR hardware). Additionally, the project should demonstrate the ability to observe very strong radio astronomy sources (eg the Sun) – the project will be undertaken in Stellenbosch, where the RFI environment is poor. The aim is to develop engineering skills in aperture array systems.

In addition to this, we wish to investigate an open source transient aperture synthesis array radio telescope (TART), developed by the University of Ontago. The system is a fully functional radio telescope and will aid the student to test various concepts, e.g. array element positioning.

In this project we propose to take the public participation in SETI to the next level and design a receiver which a hobbyist can hack easily and then use it to receive data and contribute to research. The motivation for this project are two-fold.

First of all this will help in achieving the challenging goal in SETI research to look at all the spots on sky at all the times. This is a goal which can not be achieved just using radio telescopes.

The second goal is to generate interest in the public for SETI and engineering in
general.

There are some such initiatives already existing. Most of these use software defined radio (SDR) dongles. Setileague has been a place to collaborate on such projects1.

The major limitation in such projects has been the lack of synchronisation. If individual stations (by individual hobbyists) are not synchronised then they can only act as stand-alone receivers. Given the fact that these systems will operate in RFI-heavy areas such data, thought good for generating excitement, has little contribution to science.

We plan to investigate the following aspects of HackSETI:

Is it possible to have a universal clock (either through GPS or telecommunication systems) which can help us to make independent HackSETI data streams “reliably” synchronous? If so then what kind of best and worst case SNR can we expect?

Can we upload the data from individual HackSETI systems to cloud and then do the synchronisation and beam-forming operations in a centralised server or cloud?

Can we design robust RFI filtering algorithms which the hobbyists can run insitu?

In this proposed MSc project the student shall work on the system design of a HackSETI system, implement the first prototype and analyse its performance limitations. Making a useful inexpensive instrument inherently makes any project multidisciplinary. Hence, the project will have substantial amount of work in the domains of noise analysis, data communication, signal processing, machine learning and RF circuit design.

Radio frequency interference is a major challenge in radio telescope sites. Ideally we need an algorithm which can run as close as possible to the antenna and take decision on the usability of the signal received. This will help in determining which data to store and which data not to, very early in the signal processing chain. This is crucial given the number of radio telescopes gathering signal.

This project will not try to analyse the signal for the astronomical information content. Rather, it will try to take a quick decision regarding if the signal is RFI or astronomically interesting. And if it is astronomically interesting then if there is a chance that it might be ETI signal. This is an interesting problem in the sense that probability of correct classification, Pcc is less important than the probability of false alarm, Pfa.

In this proposed MSc project the student will develop algorithms which can be run real-time on embedded systems and be used as a first hand filter to determine if a given block of signal is RFI or may have SETI and astronomically significant sources.

Marion Island, halfway between Africa and Antarctica, is one of the most remote places on Earth. With no permanent inhabitants and no continental landmass within 2,000 km, it has a pristine radio environment, with no interference visible even in the FM band. The clean environment coupled with Marion’s southern location and the upcoming solar minimum means that we have a rare chance to try to oberve the universe below 10 MHz (the lower range of the High Frequency of HF band). This is truly unexplored territory, with the current state-of-the-art dating back to the ’60s and ’70s from Tasmania. This project will build prototype antennas and receivers to be deployed to Marion to make sub-10 MHz maps. If successful, we plan to deploy an array of these antennas across Marion, allowing us to improve on the angular resolution of the best available maps by a factor of about 30.

Given the small scale of this project, the student who takes it on will be able to contribute to a wide range of work spanning both instrumentation and preliminary analysis. The student may have the opportunity to participate in the April 2018 or April 2019 voyages to Marion Island, where we will deploy the new hardware and perform on-site instrument characterisation. We anticipate deploying at least two antennas that can be correlated on a low-power FPGA board such as the SNAP boards developed for HERA that we are using for another project on Marion.

A generic digital back-end and data management system for water vapour radiometry

Overview

To develop a generic digital back-end for water vapour radiometry (independent of the monitored frequency band) that would allow for acquisition, processing, actuation / control, and suitable reporting of WVR data.

To contribute to the body of knowledge in the development of low cost, yet low-EMI digital systems suitable for use at radio astronomy sites.

The mitigation of RFI from intentional transmitters as well as unintentional transmitters is a key aspect of maintaining the quality of the MeerKAT and SKA Site for radio Astronomy.

The aim of this research topic would be to investigate the root causes of RFI from switching of different devices in various equipment, e.g. cooling or pumps. This would involve EMC measurements and data analysis as key outputs. Proposed snubber circuits which can easily be retrofitted to any device, and which mitigates the RFI significantly, without influencing the equipment functioning itself, will need to be designed, constructed and tested. This would involve solid electronics design together with EMC design principles.

The aim of this research topic would be to do characterisation measurements of typical noise sources in frequency and time domain, using conventional measurements as well as the MeerKAT Telescope. This will enable classification algorithms to identify these signatures from telescope and fixed monitoring stations data. RFI direction-finding using the telescope will form an additional part of the project. Both EMC measurements and signal and data analysis techniques would be required.

The aim of this research project is to investigate and propose an alternative EMC compliant solution for electric fences as used on farms around the SKA site. The final solution should provide an alternative smart animal sensing architecture, with a very low-frequency-content shock-pulse only conducted on the fence wire when a disturbance is detected.

Directional antennas designed for RFI and EMC purposes with large bandwidths can pose great challenges. Antenna size and robustness are important factors, especially if the antenna is required to work to relatively low frequency. The aim of this research topic would be to design a hyperband directional EMC antenna which can be used for RFI monitoring, measurements and RFI hunting. It should cover all the relevant frequencies for radio astronomy instruments on site, be electrically small and be mechanically robust.

Doctoral Research Projects: Astronomy

Understanding the Limits of Interferometric Techniques for Extended sources

Overview

Extended sources can be great sources of astronomical interest such as radio clusters found at low frequencies or the emission of our Galaxy, The Epoch of Reionisation (EoR) and intensity mappting (IM) are the next frontiers for the cosmologist. The faint signal arising from these epochs can be measured by radio interferometers at low frequencies capturing the redshifted signal from the 21cm line. However, an outstanding issue not clearly resolved by any current EoR or IM experiments is that calibration issues related to extended sources could plague this signal and prevent a clear detection from taking place. In particular, it is possible that direction dependent effects (DDEs) will change the nature of this signal and smear any possible detection.

We propose to investigate how DDEs affect these extended sources for the EoR and IM experiments and other signals at the low to mid frequencies of Meerkat and SKA1, and whether the statistical properties of these signal are maintained after DDEs are calibrated out, and more specifically if the magnitude of the fluctuations is maintained. The student would obtain simulations of the 21cm signal, pass them through a radio interferometry simulator, and obtain visibilities which would be corrupted with a direction dependent signal. This signal would be calibrated with DDsolution algorithms such as SAGECAL or StefCal, and the signal would be remeasured and compared to the original input.

Over the past two decades, strong evidence has emerged that supermassive black holes play a critical role in the evolution of their host galaxies. For massive galaxies, the stellar assembly appears to be regulated by the energy output associated with accretion onto a nuclear black hole. An important research area in galaxy evolution is therefore to characterize the accretion history of the Universe, which requires wide-area extragalactic surveys at all wavelengths. High angular resolution radio observations hold a unique advantage in their ability to disentangle AGN from star formation emission and their insensitivity to dust. Deep, high resolution radio observations over large areas have been challenging in the past, however, this has been largely overcome through new software correlator developments (the multi-phase centre correlation technique). This represents a dramatic shift in the efficiency of VLBI observations, and enables surveys of depth and area that will be a unique addition to multi-wavelength, wide-field surveys past, present and future. This is timely, given the surveydriven focus of next-generation radio interferometers such as MeerKAT and SKA-mid.

While MeerKAT’s high sensitivity and wide field-of-view will enable deep surveys over large area, these will be limited to >5 arcsec angular resolution (at 1.4 GHz), which is not sufficient to discern radio jets from star formation in galaxies beyond the local Universe. This is of key importance for a number of MeerKAT science objectives, particularly tracing the star formation rate history of the Universe and understanding the role of mechanical feedback in galaxy evolution. VLBI will also play an important role in HI emission and absorption components of the MIGHTEE and LADUMA surveys, contributing unique morphological insights to the interpretation of gas inflows and outflows that have strong complementarity with ALMA. But perhaps even more interesting will be wide-field VLBI’s ability to enable the discovery of exotic objects such as binary supermassive black holes and strong gravitational lenses.

Many MeerKAT extragalactic Large Survey Projects (LSPs) would therefore be significantly enhanced by matched sensitivity VLBI observations across a significant fraction of the selected fields. This PhD project forms part of the MIGHTEE-VLBI working group (chairs: Deane and Agudo) and will perform deep VLBI surveys over the relevant extragalactic fields. It will begin with a large VLBA dataset of the GOODS-North extragalactic field, which is already in hand. The skills and techniques developed with be directly applied to MeerKATVLBI surveys of LSP extragalactic fields. Additional survey objectives will include multi-epoch VLBI imaging in order to select sources based on their milli-arcsecond flux variability; and to incorporate e-MERLIN observations where possible to bridge the L-band uv-coverage between the MeerKAT and VLBI components, enhancing the interpretation of both. The student will actively incorporate the wide range of cutting-edge interferometric calibration and imaging algorithms in development within the RATT group.

The MeerKAT Absorption Line Survey (MALS) will observe ~1000 fields centred on quasars (740 in L-band, 370 in UHF), spread across the southern sky. The wide (~1 deg) field of MeerKAT provides an opportunity to conduct a serendipitous survey of galaxy clusters in each MALS pointing. We expect there to be about 1500 clusters with masses (M500) > 3 x 1014 M⊙ within the survey area. All MALS pointings will be within the footprint of the Advanced ACT cosmic microwave background survey (De Barnardis et al. 2016), in which MALS team members are actively involved, and which will deliver Sunyaev-Zel’dovich (SZ) masses for all clusters above this mass limit. High quality multi-band optical data will be available for the vast majority of these clusters from Dark Energy Survey, Hyper-SuprimeCam Survey, and the ESO public surveys.

We will use this large cluster sample to study the star formation activity in clusters over half the age of the Universe. The sensitivity of MALS (~5 uJy RMS) will allow individual galaxies with star formation rates (SFR) > 20 M⊙/yr at z < 0.7 to be detected at 5σ, assuming the Bell (2003) relation between SFR and 1.4 GHz luminosity. We will measure how the star formation rate per unit cluster mass evolves, and investigate how this varies with cluster mass. The clean, SZ selection of the clusters in the MALS field will simplify the interpretation of the results, by easing comparison with cosmological simulations. The sensitivity reached by the MALS observations is comparable to surveys of ~10-100s of clusters over a similar redshift range that have been conducted at 24 μm with MIPS on the Spitzer Space Telescope (Webb et al. 2013), or with Herschel at 250 μm (Alberts et al. 2014). The advantage of our survey will be the increase in the sample size by 1-2 orders of magnitude, and reliable masses based on SZ observables (previous surveys are based on IR-selected cluster samples).
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Compressive sensing (CS) theory has yielded a number of deconvolution algorithms based on the sparsity assumption of the sky that perform far better at recovering extended emission than CLEAN and its multiscale variations. In particular, the team of Y. Wiaux (Heriot Watt University), with which Rhodes has an extensive collaboration funded by the Swiss/NRF bilateral program, has produced a spate of algorithms that also incorporate multi-frequency deconvolution, as well as calibration of direction-dependent effects (Repetti et al. 2017), into a “primal-dual” optimization framework. These have been validated on real data, such as JVLA observations of Cyg A. On the other hand, our collaboration with C. Tasse (Obs. Paris) has produced DDFacet, a flexible imaging framework that is designed to readily incorporate novel deconvolution approaches. The aim of this project is to bring these two ingredients together, by porting the new CS algorithms into the DDFacet framework, and thus producing a novel imaging package with unprecedented capability to recover extended emission.

A proposed design for Baseline-dependent correlators using Farrow filters combined with the raised cosine

Overview

Baseline-dependent averaging (BDA) is a potential uv-data compression scheme that could be adopted for next generation radio telescopes such as MeerKAT and the future SKA. A large body of work has already been done regarding BDA applied to MeerKAT, VLA, EVN and LOFAR (e.g. Atemkeng et al., MNRAS 2016; C. Tasse et al., A&A, submitted; Atemkeng et al., MNRAS, in prep.). Currently, BDA can only be used post-correlation and not in real-time. The main aim of this work is to focus on a correlator design that implements BDA in real time correlations.

This project will use finite impulse response filters (FIR) (e.g. the raised cosine) and Farrow filters to implement a low pass and decimation filters to design a possible correlator work-flow for BDA. If a long baseline is down sampled, then the decimation phase filters will consist of interpolating the signal by some factor and decimate with an offset by taking the baseline-dependent delay parameters into account: this is equivalent to decompression on these type of long baselines and this will preserve uv-bins resolution. If a short baseline is oversampled, then the decimation phase filters will resample the data according to the variable delays: this is equivalent to compression.

A naive implementation would be very inefficient given that most of the decimation filters’ band will not contribute to the correlator output. An ideal FIR filter will be the one that uses as few samples as possible, has good alias rejection, and is computationally efficient. This motivates the use of Farrow filters for this project.

Doctoral Research Projects: Engineering

Numerical electromagnetic analysis has become an indispensable tool in modern antenna design. The design of the mid-frequency aperture array and other radio astronomy antennas involves very large computational electromagnetics analyses. In such cases the computational cost can quickly become prohibitive and it becomes necessary to investigate more efficient numerical methods. For this project, the candidate must firstly study cutting-edge integral equation-based methods relevant to electrically large antennas. Secondly, the most relevant of these existing, cutting-edge methods must be implemented as a computer code. Thirdly, new methods must be developed which are more efficient than the present state-of-the-art, with regards to analysis of electrically large, radio astronomy antennas. This work will likely focus on macro-basis function methods, solution error estimation and iterative solvers. This challenging project has excellent scope for journal publications.

High Frequency Transmission Line Modelling of a Low Voltage Power Cable

Overview

Modern switching electronics that employ power circuitry (convert electrical energy) or digital circuitry (process information) emit RFI. This RFI interferes with the SKA.

Switching electronics produce RFI harmonic currents that is propagated by the attached power cables. These RFI currents radiate as it use the cable as an antenna structure. See figure 1. This happens in Differential and Common Mode (DM & CM). In order to clearly describe the radiation process the current on the cable must be known. For this the switching noise harmonics and the powerline characteristics should be known. This study concentrates on the powerline characteristics. The powerline will be modelled as a classic transmission line that has Per-Unit-Length (PUL) parameters for DM and coupled PUL parameters with Multiconductor Transmission Line (MTL) theory for CM. Most of the emissions detrimental to the SKA below 1GHz are in CM.

In transmission line theory the PUL parameters of resistance (R), inductance (L), capacitance (C) and conductance (G) are independent of frequency. This is not the case in practical power cables which can have RFI flowing on it from a couple of kHz into the GHz. This study will aim to describe the frequency dependent transmission line PUL parameters as basis for characterising low voltage power cables and use MTL theory to describe CM behaviour. Ultimately a low voltage powerline cable is a multi-core structure (Live, Neutral and Earth cores above a ground) and only MTL theory can describe this.

All modern electronics that either employ power circuitry (convert electrical energy) or digital circuitry (process information) emit RFI. Understanding and being able to use a model for this phenomenon and knowing how it interferes with the SKA is of prime importance. It will enable scientists and engineers to:

Predict RFI from switching electronics

Design and build “quieter” / lower RFI circuitry

Better determine the RFI influence on the SKA

Electronics in the vicinity (up to kilometres) of a radio telescope degrades the observed data. The most general case is where a circuit switches, produces a spectrum of conducted harmonics on an attached cable (which acts as an antenna) and them radiates RFI which is “seen” by the telescope.

Attached figure 1 shows a “big picture” of this process and the proposed area of study. It shows a noise source interfering with a receiver via for example attached cables and electromagnetic radiation. This process is not trivial since noise generation and radiation takes place in both Common Mode (CM) and Differential Mode (DM). DM is per the normal circuit between a conductor and its return while CM is between all the conductors as a whole and a common ground. DM and CM are dependent on geometry, parasitics, frequency and material characteristics.

Although DM noise has been well studied, CM noise generation and propagation remains largely obscure. Of specific importance is the generation of CM RFI inside electronic systems and its propagation on attached cables that act as antennae. Up to a couple of GHz, common mode radiation is the dominant mode of EM emission and should be known in its entirety.

This study aims to contribute to science by:

Describing DM noise and RFI generation inside electronic systems.

Describing the conversion mechanisms of DM to CM (due to imbalance and parasitics) at circuit level.

Array antennas, including mid frequency aperture arrays (MFAA), as well as phased array reflector feeds (PAF), are attractive antenna alternatives for the second phase of the SKA project due to their high levels of flexibility. However, designing high fidelity (high sensitivity, controlled sidelobes and cross polarization, etc.) array antennas with wide operating bandwidths (of more than an octave) remains a difficult problem.

Given the wide range of science goals of the SKA, however, some trade-offs between different performance metrics of array antenna systems must be considered. This is normally a difficult task since much of the information might not be available in detail beforehand.

A solution to this issue is to perform formal multi-objective optimization (MO) of the antennas, so that the system engineer has access to the exact trade-off levels encountered for each antenna technology. Traditional methods of performing such optimizations are computationally prohibitively expensive, due to the long simulation times of full wave solvers, and the very large number of evaluations required to properly explore the (often high dimensional) design space. Surrogate based optimization (SBO) is a technique well suited to solve such problems. Here a coarse model is sought, which is fast to evaluate, but still relatively accurate and based on the physical fine simulation model. A surrogate model is constructed by aligning the coarse and fine models in sub-regions of the design space – normally close to the desired optimum (or Pareto front in MO problems).

The goal of this project is to develop surrogate models, for use in MO-SBO, specifically tailored to radio telescope array antennas. Once these models are available the full trade off space, or so called Pareto front, for all the performance metrics of the antennas may be calculated. The Pareto fronts will provide quantitative information on the performance limitations of different technologies.

Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA. Wavelength Division Multiplexing refers to the transmission of multiple optical fibre wavelengths within a single optical fibre. Flexible spectrum refers to the fact that the channel wavelength assignment is not statically fixed,
but is dynamically optimized in real time to ensure optimum network performance at all times. In order for these networks to function optimally, novel hardware and dynamic algorithms need to be identified and developed to perform critical tasks. Such tasks include wavelength assignment, signal routing, network restoration and network protection. This project focuses on developing, implementing and testing modulation formats, hardware technologies and algorithms for optimizing the operation of such networks.

Applying algebra to study the properties of graphs is a classic area of research in mathematics. With the advent of big-data type challenges the use of graph is gathering interest amongst the data processing engineers. This follows from the fact that bigdata mostly originates because of a large number of sensing nodes. Some of the recent works have looked into developing signal processing framework based on graphs [1,2]. Tools, inspired by such work, has shown much promise [3, 4].

Representing astronomical data as a graph at each instant of data-capture is intuitive. Hence, we hypothesize that by exploring ways to 1) represent (e.g. [5]) and 2) manipulate (e.g. [6]) the astronomical recordings in a graph framework will help not only in presenting an elegant framework to handle and store massive amount of data, it will also help in making the data analytics processes more robust and less prone to noisy and false recognition-results.

In this proposed PhD project the student will work on the hypothesis that using algebraic graph theory based approaches will make astronomical data handling and processing faster and more robust.

To evaluate the electromagnetic properties of materials across a wide band is not trivial. Different techniques apply to different frequency ranges. The available methods covering all the frequency ranges for SKA would need to be investigated, evaluated and tested. Methods include (in increasing frequency), Coaxial test methods, Coaxial single probe methods, Free Space Setups, Waveguide Setups and Radar Cross Section Methods.

The design and calibration of setups for these measurements would be required, as well as the development/adaptation and implementation of the relevant equations to extract the electromagnetic properties. As example, soil properties have been notoriously difficult to measure. The measurement techniques used here will be relevant for the evaluation of different shielding materials, where the concomitant part of the project
will include the development of alternative materials for shielding and EM miniaturization purposes.

SARAO

The South African Radio Astronomy Observatory (SARAO) is a National Facility managed by the National Research Foundation and incorporates all national radio astronomy telescopes and programmes. Find out more